This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7 119 from an application entitled LONG BAND FIBER AMPLIFIER USING FEEDBACK LOOP earlier filed in the Korean Industrial Property Office on the day of Jul. 22nd 1999, and there duly assigned Serial No. 29827/1999, a copy of which is annexed hereto.
1. Technical Field
The present invention relates to a fiber amplifier of an optical communication system, and more particularly to a fiber amplifier of a long band (1575 nanometersxcx9c1605 nanometers) used for widening an amplification band of a fiber amplifier.
2. Related Art
Wavelength division multiplex (WDM) transmission is an information transmission scheme using optical fibers in which the wavelength area of an optical fiber is separated into a plurality of channels, the channels are multiplexed, and thus signals at different wavelengths are transmitted through the optical fiber at the same time, to thereby increase information transmission capacity.
A plurality of optical amplifiers are used between a transmitter and a receiver in a wavelength division multiplex transmission system to compensate for signal attenuation resulting from long distance transmission. The efficiency of optical amplifiers is important for transmission of optical signals.
I have found that it would be desirable to increase optical amplification efficiency. Efforts have been made in the area of optics and feedback loops.
Exemplars of recent efforts in the art include U.S. Pat. No. 5,239,607 for Optical Fiber Amplifier with Flattened Gain issued to da Silva et al., U.S. Pat. No. 5,455,835 for Article Comprising an Optical Waveguide Laser issued to Atkins et al., U.S. Pat. No. 5,153,933 for Apparatus for Generating a Comb of Optical Teeth of different Wavelengths issued to Smith et al., U.S. Pat. No. 5,117,196 for Optical Amplifier Gain Control issued to Epworth et al., U.S. Pat. No. 5,088,095 for Gain Stabilized Fiber Amplifier issued to Zimgibl, U.S. Pat. No. 5,128,800 for Gain Switchable Optical Fiber Amplifier issued to Zirngibl, U.S. Pat. No. 6,031,660 for Analog/Digital Double Automatic Power Controlling Device in an Optical Fiber Amplifier issued to Park et al., U.S. Pat. No. 5,245,690 for Optical Fiber Amplifier Including Rare Earth Doped Fiber And Feedback Pump Light Source Control issued to Aida et al., U.S. Pat. No. 6,016,218 for Optical Fiber Amplifier issued to Jo et al.
While these recent efforts provide advantages, I note that they fail to adequately provide an L-band (long band) optical amplifier using a feedback loop increasing amplification efficiency.
Accordingly, the present invention has been made in an effort to solve the problems occurring in the related art, and an object of the present invention is to provide along-band (L-band) erbium doped fiber amplifier which can increase the amplification efficiency in the L-band, so that the communication capacity is increased in developing a fiber amplifier having a long amplification band.
It is another object of the present invention to provide an L-band erbium doped fiber amplifier which can reduce the manufacturing cost thereof.
It is still another object of the present invention to provide an L-band erbium doped fiber amplifier which can improve the gain evenness according to the wavelength of the signal light.
In order to achieve the above objects, according to the present invention, there is provided an L-band fiber amplifier comprising a rare earth doped fiber as an amplification medium, forward and backward pump laser diodes, positioned on front and rear ends of the rare earth doped fiber, respectively, for generating pumping lights, first wavelength selective couplers for providing the pumping lights from the pump laser diodes to the rare earth doped fiber, optical isolators, inserted into front and rear ends of the first wavelength selective couplers, respectively, for intercepting backward propagation of signal lights reflected from input and output terminals of the fiber amplifier, a feedback loop for making a seed beam incident to the rare earth doped fiber or making an amplified spontaneous emission (ASE) incident again to the rare earth doped fiber, second wavelength selective couplers, provided between the optical isolators and the first wavelength selective couplers, respectively, for making the seed beam incident to the feedback loop or extracting and providing the ASE to the feedback loop, and a filter, connected to the feedback loop, for filtering a specified wavelength of the seed beam or the ASE.
In another aspect of the present invention, there is provided an L-band fiber amplifier comprising a rare earth doped fiber as an amplification medium, forward and backward pump laser diodes, positioned on front and rear ends of the rare earth doped fiber, respectively, for generating pumping lights, first wavelength selective couplers for providing the pumping lights from the pump laser diodes to the rare earth doped fiber, optical isolators, inserted into front and rear ends of the first wavelength selective couplers, respectively, for intercepting backward propagation of signal lights reflected from input and output terminals of the fiber amplifier, a feedback loop for making a seed beam incident to the rare earth doped fiber or making an amplified spontaneous emission (ASE) incident again to the rare earth doped fiber, second wavelength selective couplers, provided between the optical isolators and the first wavelength selective couplers, respectively, for making the seed beam incident to the feedback loop or extracting and providing the ASE to the feedback loop, a filter, connected to the feedback loop, for filtering a specified wavelength of the seed beam or the ASE, and an optical attenuator, connected between the second wavelength selective coupler and the filter, for attenuating a strength of the seed beam or the ASE to adjust a gain evenness of a source output.
The present invention is more specifically described in the following paragraphs by reference to the drawings attached only by way of example. Other advantages and features will become apparent from the following description and from the claims.